The development team has released a new iF0rce tweak “SiriOus” which allows iOS devices older than 4S dictation of text, just like the original Siri.
Here is the guide to enable this feature on the iPhone 4, iPod Touch 4G and iPhone 3GS jailbroken:

– Open Cydia and add one of the following repository:http://apt.ifOrce.com http://siriforyou.bplaced.net/repo/– Install the tweak “SiriOus”

To prove that you just have to open any application that supports writing from the keyboard.
The dictation will be able to activate it from a small little key on the left of the spacebar.
The interface is the same in all respects to that of thisSiri on the iPhone 4S.

The installation of SiriOus requires the respring of the device.
If during this operation, the device is locked, do not perform the restore boot! Use iFunBox, iPhone Explorer or SSH to remove the framework “AssistantServices” in the directory “/ System / Library / PrivateFrameworks” of the device.